To this day, opinions differ as to whether or not scrambling fighter jets was considered standard procedure in air emergencies at the time of the attacks or whether, as Popular Mechanics argued in March 2005, this was something rare and extraordinary. In their cover story “Debunking 9-11 Lies,” they tried to explain NORAD’s delays and failures by pointing out lamely that "in the decade before 9/11, NORAD intercepted only one civilian plane over North America: golfer Payne Stewart's Learjet, in October 1999 […] it took an F-16 1 hour and 22 minutes to reach the stricken jet. […] Prior to 9/11, all other NORAD interceptions were limited to offshore Air Defense Identification Zones (ADIZ). The ADIZ areas seem to be a sort of moat 'round the castle, where incoming international flights are made to identify themselves or risk being taken out. They run along the East and West Coasts and along the Mexican and Canadian borders. "Until 9/11 there was no domestic ADIZ," FAA spokesman Bill Schumann told the magazine. 
They would probably have liked to say there were no intercepts at all over continental airspace, but had to cede the one instance after it was pointed out in the factual record by 9-11 revisionists, an errant plane that crossed no borders or ocean shores and yet triggered a fighter escort. On October 26, 1999, famous pro Golfer Payne Stewart was flying in his private Learjet when the cabin lost pressure and killed all on board. The plane continued on autopilot across several states, trailed by fighter jets until it finally crashed in North Dakota. The shoot-down option was publicly addressed at the time: The Washington Post reported “Pentagon officials said they never considered shooting down the Learjet” because, according to a senior defense official, ‘the (FAA) said this thing was headed to a sparsely populated part of the country, so let it go.’”  Now, if it had been a hijacked 757 headed for New York after one plane had already crashed into the World Trade Center…
But was this the only fighter intercept ever ordered over the continental U.S.? If intercepts simply weren't done over the mainland, why was an exception made in this one case and this one case alone? Or did they mean this was the only intercept over America that made the news? According to an article in the Calgary Herald-Tribune from a month after the attack, fighter interception for stray aircraft actually was a weekly occurrence even before 9-11: “Today […] fighter jets are scrambled to babysit suspect aircraft or "unknowns" three or four times a day. Before Sept. 11, that happened twice a week. Last year, there were 425 unknowns -- pilots who didn't file or diverted from flight plans or used the wrong frequency. Jets were scrambled 129 times.”  Was every one of these 129 intercepts in the year 2000 over the ocean in ADIZ areas, with none over the continental U.S.? And in the nine years before that too, with the exception of one famous golfer?
Common sense and some evidence indicate otherwise. One of the fighter pilots that was scrambled on 9-11 said in a BBC documentary on his first notification of trouble “they said the Tower [was] calling and something about a hijacking. It was flight American 11, a 767, out of Boston going to California. At the time we ran in and got suited up… It's just peacetime. We're not thinking anything real bad is going to happen out there.” The narrator of the documentary adds “neither pilot at this time has any reason to believe that this is other than a routine exercise.” 
This was at some point before American 11 ended – we were still in pre-9-11 peace time, if the last minutes of it, and he knew to get suited up (that is, ready for takeoff) in response to the hijacking of a trans-continental flight. This sounds like a routine, standard procedure scramble and intended intercept over continental airspace to me. Perhaps the Payne Stewart case is not so anomalous after all.
 Chertoff, Benjamin et al. “Debunking 9/11 Myths.” Popular Mechanics. March 2005.
 Walsh, Edward and William Claiborne. “Golfer Payne Stewart Dies in Jet Crash.” Washington Post. October 26, 1999. Page A1.
 Slobodian, Linda. “NORAD on Heightened Alert.” The Calgary Herald. October 13, 2001.
 BBC Video. Clear the Skies. First Aired September 2002.